Polymers containing hydantoin groups and processes for their preparation have already been disclosed (DE-AS (German PUblished Specification) No. 1,570,552 and DE-AS (German Published Specification) No. 1,795,751). They are used as temperature-resistant wire enamels or for the production of temperature-resistant films. In spite of the remarkable property level of these polyhydantoins, they are not suited for all uses in the modern electronics industry. Thus, high temperature-resistant films are required for flexible printed circuit boards in electronic circuits. Such films are permitted to exhibit only a very low shrinkage during processing at temperatures above 200.degree. C. in a solder bath. However, this requirement is only inadequately fulfilled by films of hitherto known polyhydantoins. The desire therefore existed to develop polyhydantoins which exhibit only a very small shrinkage at temperatures above 200.degree. C.